Oilfield drilling, stimulation, and production activities often cause microseismic events due to compacting rock, propagating fractures, or relieving of shear stress. For example, drillers may perform a hydraulic fracturing operation in which a fluid is injected into a borehole under high pressure to enlarge any existing fractures in the formation and to create new fractures. The injected fluid often carries entrained particulate matter to be deposited in the fractures, thereby propping them open when the pressure returns to normal. Such fractures substantially increase the permeability of the formation, which makes it easier for fluid to flow from the formation into the borehole.
Microseismic events from the hydraulic fracturing operation cause pressure and/or shear waves to propagate outward in all directions away from the events. Receivers up to a kilometer away have been used to detect and locate such microseismic events in rock types such as unconsolidated sands, chalks, and crystalline rocks by sensing the waves. The spatial distribution of microseismic events may be used to determine information about the chemical, hydraulic, and/or mechanical processes occurring in the in the earth.
The economic success of hydrocarbon extraction is heavily dependent on fracture complexity and subsurface insight with regards to pay zones. As such, oilfield operators employ models to predict the effects of a fracturing operation and, in some cases, employ micro-seismic detection to gather data for the models. One of the primary uses of microseismic data is determining the fracture geometry and providing an estimation of stimulated reservoir volume (SRV). SRV is the total volume of rock which has been fractured and is presumed to be permeably connected to the borehole. Because of the complexity of measuring SRV in a heterogeneous formation, SRV estimates can vary widely. As such, decisions based on SRV, which include the economic feasibility of extraction, may have an undesirably high uncertainty.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.
Notation and Nomenclature
Certain terms are used throughout the following description and claims to refer to particular system components and configurations. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. In addition, the term “attached” is intended to mean either an indirect or a direct physical connection. Thus, if a first device attaches to a second device, that connection may be through a direct physical connection, or through an indirect physical connection via other devices and connections.